Sexual conflict/ the evolution of parental care Flashcards
DIfferences between male and female strategies
Male:
- Large intrasexual variation in total reproductive success (T) determined by competitive accesses to females. Strong sexual selection.
Females:
- Small intrasexual variation in total reproductive success determined by intrasexual competition for the ‘best’ males. Week sexual selection.
Parental investment
Any investment by the parent in an individual offspring that increases the offspring’s chance of surviving (and hence reproductive success) at the cost of the parent’s ability to invest in other offspring.
Sexual selection and parental investment
The differences in sexual selection in males and females also impacts the difference in parental investment.
Females are predisposed to invest more into parental care than males.
Females are more selective in their mate choice and invest more into each offspring (reproduction limited by ova). Males invest in multiple partners and invest less in each offspring (reproduction limited by number of mates).
Females invest more in producing and caring for offspring, and are generally more limited in the number of offspring they can produce compared to males.
The difference in reproductive potential and the fact that females invest more in each offspring create a scenario where females are more selective in mate choice, and their reproductive success is more dependent on the quality of mates and the resources they provide.
Males, on the other hand, may benefit more from mating with multiple partners and investing less per offspring, as their reproductive success is often limited by access to mates.
Other factors promoting maternal investment:
- Males do not want to invest as they cannot gauruntee paternity.
- Males are able to escape and care as females often bare the offspring/ required to bring up (e.g. milk)
Knock on affect of increased maternal care (operational sex ratio)
Increase maternal care increases the ‘time out’ period where the mother is caring for her offspring and unable to mate.
This changes the operational sex ratio (ratio of sexes availiable to mate)-> Male biased.
A change the OSR increases the strength of sexual selection in the males due to increased competition for females.
This further promotes maternal investment.
Sexual selection leading to sex rules and the exception that proves the rule.
The males (sex competing for mates) are selected to mate multiply rather than invest in parental care while females (sex not competing) are selected to invest in parental care and partner choice rather than remating.
Sex roles reversed: Spotted Goby males
- Spotted Goby males disappear over the season due to predation leading to competition among females for mates.
- This competition results in increased paternal care
Sexual conflict
Irreconcilable divergence in fitness interests of individual males and females, which cannot be maximised simultaneously by the same reproductiven decision
Anisogamy predisposes one sex to stronger sexual selection, creating divergent reproductive strategies and fitness interests in males and females.
- Males want to mate as much as possible
- Females are selective with who they want to mate with
Conflict can arise over decisions at multiple stages of the reproductive process.
- Mating decisions
- Mating duration and sperm insemination
- Remating rate
- Abortion and infanticide
Sexual conflict: Mating decisions
Coercion
- Males can overcome female disrcimination for mates through sexual harassment and coercion which can harm females.
Example: male ducks can drown female ducks when trying to mate with them
Example: traumatic insemination in bed bugs where male peirces female abdomin wall with his genitalia -> females unable to avoid insemination -> show little resistance
Sexual cannibaism:
- Females can consume males before, during or after mating to prevent mating
- Or as a resource post mating -> mantise
Sexual conflict: Mating duration
There is a conflict over the length of mating, as males want to maxmise the liklihood or fertilisation and females want to avoid fertilisation.
Example: seed beetles
- Female seed beetles interrupt mating by kicking the males off their back
- Males have evolved a geneitalic spine that wounds the females reproductive tract
Sexual conflict: sperm insemination
Males and females have a conflict over the insertion and maintainance of sperm into the females.
Example: Hermaphrodites
- Individuals simualteously produce sperm and eggs however, it is more beneficial to fertilise someone elses eggs than have you own fertilised.
- Snails shoot love darts that manipulate partner into accepting sperm
Example: female ejection or neutralisation
- Females can eject or nautralise sperm once it has been inserted to stop fertilisation
- Males have evolved copulaton plugs to stop ejection
Sexual conflict: remating decision conflict
Males do not want females to remate to avoid sperm competition.
Example: Cocktail of proteins in Drosophila
- Drosophila ejaculate contains a cocktail of proteins which inhibits female propoensity to mate for 48 hours to reduce competition of the sperm
- Cocktail also increases ovulation rates
- This cocktail reduces the liftime fitness of the females
Sexual conflict: Abortion and infanticide conflict
Females can try to abort the zygotes following fertilisation and resorb nutrient for later fertilisation events
Example: Guppys shown to absorb embryo following fertilisation with undesirable male
Some males kill the offspring of the females to promote a new oestrus cycle in females.
The role of population structure in sexual conflict
Sex ratio
- The more male biased the sex ratio, the greater the sexual conflict and the more agressive the males.
- Greater agression causes the females to die excalating conflict further.
- This cycle can lead to extinctions
Dispersal
- Sexual conflict and agression is increased where dispersal is limited as the females are unable to escape.
- If females are able to disperse, male agression can lead to a reduction in male success
- Example: Frogs being connected between ponds
Male- male competition leading to the harm of females
As well as male competition making males more aggressive it also has other effects:
Polyspermy due to multiple mating can lead to embryo failure
Males can strategically harm females:
- Sexual punishment to ensure they cooperate
- Harm to reduce their linklihood of reproducing again so that they invest more into this reproductive event.
Example: Sperm injection into bedbugs also injects bacteria. The more mates a female has, the higher their risk, promoting singular mating.
Antagonistic co-evolution
Inter locus conflict promotes antagonistic co-evolution/ arms race.
If different loci (in males and females) have different optima then there will be an arms race between the traits.
Example: Ducks
- Female ducks have increasingly complex reproductive tracts and male ducks are evolving increasingly complex reproductive organs to allow them to mate with the females.
Co-evolution often leads to exageration of traits as they become more complex.
Females evolve to me more resistant to males and males evolve to be maore harmful to females
Example: Drosphila
- Study compared ancestral drosophila to sexually selected, evolved drosphila and found that the evolved male forms dominated the ancestral female forms and evolved female forms resisted the ancestral male forms
Summary
Anigosamy in the gamete of males and females means that sexual selection is greater in males than it is females.
There is more variation in male reproductive success than female as there success increases as a function of number of females mated with. However, female reproductive success is limited by the number of ova so does not increase with the number of mating events.
As a results there is greater selection on males (through male- male competition and female mate choice) as they want to maximise how many females they mate with. Females are more invested in chosing the optimum mate and invest more into each reproductive event.
The increased sexual selection in males also leads to reduced parental investment. They invest little into many reproductive events to maximise their reproductive success, unlike females who invest a lot into few reproductive events to maximise reproductive success.
The ‘sex roles’ of males and females also lead to sexual conflicts which occur at every stage of reproduction
- Sperm incemination
- Mating choice (coercion and cannabilism)
- Mating duration
- Abortion and infanticide
- Remating rate
As well as agression during these different stages of conflict, males can stratgically harms females to get them to cooperate or to make them invest more into reproduction as they will not reproduce again.
Differential optima of males and females leads to an antagonistic arms race
Example: genitalia of ducks
